In centrifugal separators for cleaning of gaseous fluids, wherein the conical disc elements of the rotor have a relatively small difference in radius between their outer and inner peripheries, i.e. where the flow distance of the fluid through the channels between the disc elements is relatively short, the fluid has a tendency to create flow disturbances when entering rotating, radial flow channels between the disc elements, which affects the effective separation ability of the channels. Such disturbances can have the form of sub pressure zones created behind the radial ribs forming the channels between the disc elements, whereby the sedimentation area for the particles of the gaseous fluid is reduced substantially as is the separation capacity.